Ventilation systems for vehicles are increasingly complex as the demands on the degree of control of such systems increase. Heating, ventilation and air conditioning (HVAC) systems are typically used to control the environment in a vehicle such that desired interior conditions set by the operator are maintained irrespective of the exterior environment.
Furthermore, it is often desirable to separately control different environmental zones in the vehicle, so that each passenger may adjust the local environment conditions individually. This leads to the development of for example 2-zone and 4-zone HVAC-systems in vehicles.
However, a problem introduced by the increased complexity of the system is that it becomes more difficult to both design and control such systems. In particular, it is desirable to individually control the air flow from each outlet. Traditionally, the system has been modeled using transfer functions developed by measuring combinations of flap position and air flow in a physical model of the system such as a prototype.
As the number of outlets, and flaps, increase, the number of possible combinations increases to the extent that measurements of all relevant combinations become very time consuming. An alternative approach is to use computational fluid dynamics (CFD) calculations to build a model of the system. However, CFD-calculations are both time consuming and computer intensive.
A further disadvantage of the suggested approaches is that each modification or alteration of the system requires new measurements or calculations as the characteristics of one part of the system depend on the whole of the system.
Furthermore, it is desirable to reduce the computational resources required in the vehicle for controlling the system. Accordingly, there is a need for a model of a HVAC-system which is easier to use, both for the purpose of designing such a system and for simplifying control of the system.